This invention relates generally to an electrically-operated throttle actuator which adjusts the degree of opening of a throttle valve by the use of an electronically-controlled motor to change an amount of intake air into an engine, and more particularly to an electrically-operated throttle actuator which is designed to prevent a rotational force of the motor from being transmitted as a reaction force to an accelerator pedal.
There is an electrically-operated throttle actuator in which the operation of an accelerator by an operator (driver) is effected independently of the rotation of a motor (which operates a throttle), and a throttle valve is opened by the combination of these two operations. In such an electrically-operated throttle actuator, even if an electronic control device is subjected to malfunction, the throttle valve can be fully closed when an amount of operation of the accelerator is rendered to zero. Therefore, generally, such an electrically-operated throttle actuator is provided with a mechanical fail-safe mechanism. An example of such a drive mechanism is a differential mechanism as disclosed in Japanese Patent Unexamined Publication No. 63-55333.
The differential mechanism as disclosed in Japanese Patent Unexamined Publication No. 63-55333 includes many gears, and is complicated in construction, and requires much time and labor for assembling it. Therefore, such a differential mechanism is expensive. Another problem is that when only the motor is driven while keeping the amount of operation of the accelerator constant, a reaction force of the motor is transmitted to the accelerator pedal, so that the operator has a strange sensation.